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Very true. In my opinion, the slope and amplitude of the bass above F3 is far more important than the actual F3 value. How much of your music actually has significant content at the actual F3 value? Almost all music has significant content at many levels above F3.

Things like enclosure volume, material, and shape; woofer cone area, Qes and Qms, slope above and below resonance, phase, and group delay are just some of the factors affecting the sound of the bass in a given room. These items are difficult to quantify, but when they are right, you will know.

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Vas (which is a cubic volume of air that's equivalent to the suspension's "softness", commonly given in cubic feet (here in the good ol' U.S.A.) or in Liters (everywhere else in the world - which is where a LOT of our drivers come from)

You're thinking (or maybe not) of Cms, the compliance of the suspension system. Cms is a direct measure of the suspension softness/stiffness in units of length/unit force. Vas is calculated in part from Cms because Vas takes into account the radiating area of the driver, which is the missing part in your description, and a necessary part. Vas describes an equivalent volume of air at STP, that when acted on by an piston with the same radiating area as the driver in question, will have the same compliance Cms, or equivalently stiffness, Kms as the driver does in free-air.

Vas = k * Cms * SdČ, where k is a constant depending on whether you use imperial or S.I units.

While technically correct I wouldn't use the term damping when describing Q, as damping also refers to something else entirely. For the sake of not making a confusing subject even more so I prefer to use the term losses.

I personally like to use the terms "resonance magnification" for Q. I always liked the description: High Q systems tend to "ring" more freely, because there are less losses, because the driving force is not damped as much by it's constituents (Qms/Qes). Low Q systems "ring" less and the output is reduced because there is more losses and/or damping. Potato potato.

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Too high falutin' for me. Loss is more descriptive of why it does what it does without having to look up what resonance magnification means. Besides which resonance magnification doesn't apply to all of the various Q elements, Qp, Qa and Ql for instance.

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Too high falutin' for me. Loss is more descriptive of why it does what it does without having to look up what resonance magnification means. Besides which resonance magnification doesn't apply to all of the various Q elements, Qp, Qa and Ql for instance.

Quite true, I guess I was more referring to the Q parameters of a loudspeaker because it is more "proportional" (for lack of a better word) to the un-assisted output behavior around the low-corner, IOW, higher Q ≈ higher output potential, lower Q ≈ lower output potential, when everything else is held constant.

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Here's your scenario:
Grey curve: RS180-4 in 1.4cf tuned to 30Hz.
Green: DC200-8 in 1.6cf tuned to 30.
Yellow: Each DC160-8, each in its own 0.5cf box, each tuned to 30Hz.

Example 2:
Grey curve: RS180-4 in 1.6cf tuned to 30Hz.
Green: DC200-8 in 2.3cf tuned to 30.
Yellow: Each DC160-8, each in its own 1.3cf box, each tuned to 30Hz.

#3: (SAME driver, in 3 diff. boxes, EACH one tuned to 30Hz.)
Grey curve: RS180-4 in 1.6cf tuned to 30Hz.
Green: RS180-4 in 2.3cf tuned to 30.
Yellow: Each RS180-4, each in its own 0.5cf box, each tuned to 30Hz.

So . . . it's not just the tuning, but the comb. of Fb and Vb that determines the rolloff curve.
If you make a box too big, you get more "ripple" (roller-coaster).
If you make it too small, you drop bottom end reach.
It's very complex, and there're an infinite number of possibilities, which is why you want to use a box modeling program to target the response that YOU want.

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So far I've pretty much spent the day reading as much as I can on what everyone has suggested reading. I've built many speakers over the past 15 years but they have always been other people's designs to where I just simply buy the drivers, crossover components and build the enclosures. I've put off all this time learning about T/S parameters simply because, to me, all those numbers seem extremely overwhelming and almost intimidating if you will. I enjoy this hobby a great deal and I get a lot of satisfaction out of building my own pair of speakers. I guess I've come to the point where I'm going to just do the homework and try to fully understand everything and maybe try to come up with some of my own designs, which is what I've always wanted to do for years. Thanks again for all your comments every one of them has helped.

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I'm still confused. I was looking at the PE Solstice kit which uses two 6-1/2" woofers and i think is tunf to 30hz. I came across another design, Zaph Audio's ZRT two way ported design which uses a 7" woofer and is tuned to 30hz. From what you are all saying the bass output of these two designs will be completely different? I dont hang out in speaker forums every day so my knowledge about speaker design is limited. Im trying to learn. To me it makes no sense why the amount of bass would be different. An explanation of things in more layman's terms perhaps would be a little more useful to me. I do appreciate all of the responses though it helps me learn.

Sensitivity depends on the drivers. max SPL depends on their swept volume. the output at tuning depends on the size of the port. Smaller port will create more compression at higher SPL's. So, if you want it loud and want to still maintain your tuning frequency then you need a large, and probably very long port. All of these are factors. You can't just say tuned to 30 Hz, you're leaving out too many variables. The MLTL design with the large slot port on the Solstice keeps up with the woofers very well.

Comment

You're thinking (or maybe not) of Cms, the compliance of the suspension system. Cms is a direct measure of the suspension softness/stiffness in units of length/unit force. Vas is calculated in part from Cms because Vas takes into account the radiating area of the driver, which is the missing part in your description, and a necessary part. Vas describes an equivalent volume of air at STP, that when acted on by an piston with the same radiating area as the driver in question, will have the same compliance Cms, or equivalently stiffness, Kms as the driver does in free-air.

Vas = k * Cms * SdČ, where k is a constant depending on whether you use imperial or S.I units.

I personally like to use the terms "resonance magnification" for Q. I always liked the description: High Q systems tend to "ring" more freely, because there are less losses, because the driving force is not damped as much by it's constituents (Qms/Qes). Low Q systems "ring" less and the output is reduced because there is more losses and/or damping. Potato potato.

Comment

So far I've pretty much spent the day reading as much as I can on what everyone has suggested reading. I've built many speakers over the past 15 years but they have always been other people's designs to where I just simply buy the drivers, crossover components and build the enclosures. I've put off all this time learning about T/S parameters simply because, to me, all those numbers seem extremely overwhelming and almost intimidating if you will. I enjoy this hobby a great deal and I get a lot of satisfaction out of building my own pair of speakers. I guess I've come to the point where I'm going to just do the homework and try to fully understand everything and maybe try to come up with some of my own designs, which is what I've always wanted to do for years. Thanks again for all your comments every one of them has helped.

Getting into this, can be very confusing. If I were you I would check out this WINISD Tutorial, if you are a visual person, this can be very helpful in breaking it down for you.